Variable displacement vane pump

ABSTRACT

A variable displacement vane pump has a pump body, a driving shaft rotatably supported by the pump body, a rotor rotatably driven by the driving shaft, a plurality of vanes radially extendably installed in respective slots arranged in a circumferential direction in the rotor, a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes. At an outer circumference side of the cam ring inside the pump body, a seal member is provided and defines a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases. Then, a control valve controls only a pressure of the second hydraulic pressure chamber.

BACKGROUND OF THE INVENTION

The present invention relates to a variable displacement vane pump for power steering system.

In recent years, there have been proposed and developed various variable displacement vane pumps. One such variable displacement vane pump has been disclosed in Japanese Patent Provisional Publication No. 6-200883 (hereinafter is referred to as “JP6-200883”). In JP6-200883, a cam ring that defines a pump chamber moves (or rocks or tilts) inside an adapter ring, and by this movement, a discharge amount of oil or pressurized fluid is changed. The amount of movement of this cam ring is varied by difference of pressure between first and second hydraulic pressure chambers which are formed at both sides of the cam ring. Further, pressures of these first and second hydraulic pressure chambers are regulated by means of a control valve.

SUMMARY OF THE INVENTION

In the above variable displacement vane pump in JP6-200883, when the discharge amount has to be increased, the pressure of the first hydraulic pressure chamber is discharged to an inlet side, and thereby lowering the pressure of the first hydraulic pressure chamber. Then, the cam ring rocks or tilts toward the first hydraulic pressure chamber, and the discharge amount can be increased. However, in this case, since the pressure of the first hydraulic pressure chamber is discharged to the inlet side, high pressure is removed from the first hydraulic pressure chamber. Because of this, it takes time to increase the discharge amount, that is, a time lag occurs, and a discharge response might be delayed. In particular, in a case where the vane pump is used as a hydraulic pressure source for the power steering system, an increase of a steering load due to the response delay comes to the fore.

It is therefore an object of the present invention to provide a variable displacement vane pump which can improve the discharge response delay.

According to one aspect of the present invention, a variable displacement vane pump comprises: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring; and a control valve controlling only a pressure of the second hydraulic pressure chamber.

According to another aspect of the invention, a variable displacement vane pump comprises: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; and a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring, and the rocking motion of the cam ring is controlled by controlling only one pressure of the second hydraulic pressure chamber from the first and second hydraulic pressure chambers.

According to a further aspect of the invention, a variable displacement vane pump comprises: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring; an orifice provided on an oil passage that communicates to the outlet port; and a control valve into which a differential pressure between upstream and downstream of the orifice is introduced, and the control valve does not controls the first hydraulic pressure chamber but controls the second hydraulic pressure chamber.

According to a still further aspect of the invention, a variable displacement vane pump comprises: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring; an orifice provided on an oil passage that communicates to the outlet port; and a control valve into which a differential pressure between upstream and downstream of the orifice is introduced, and the control valve controls only a pressure of hydraulic pressure chamber that is located at the side where the discharge amount decreases by the rock of the cam ring and into which a control pressure is introduced, from the plurality of the hydraulic pressure chambers formed in the space outside the outer circumference of the cam ring.

The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view in an axial direction of a vane pump according to an embodiment 1 (a control pressure is introduced into a second hydraulic pressure chamber).

FIG. 2 is a sectional view in a radial direction of the vane pump according to the embodiment 1 (an eccentricity amount of a cam ring is maximum).

FIG. 3 is a sectional view in a radial direction of the vane pump according to the embodiment 1 (the eccentricity amount of the cam ring is minimum).

FIG. 4 is a sectional view in a radial direction of the vane pump according to an embodiment 2 (a control pressure is introduced into a third hydraulic pressure chamber).

FIG. 5 is a sectional view in a radial direction of the vane pump according to an embodiment 3 (a third hydraulic pressure chamber is defined by a third seal member).

FIG. 6 is a sectional view in a radial direction of the vane pump according to an embodiment 3-1.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be explained below with reference to the drawings.

Embodiment 1

[Structure of Vane Pump]

An embodiment 1 will be explained with reference to FIGS. 1 to 3. FIG. 1 is a sectional view in an axial direction of a vane pump 1. FIGS. 2 and 3 are sectional views in a radial direction of the vane pump 1. FIG. 2 shows a case where a cam ring 4 is located or positioned at an end in the negative direction of y-axis (an eccentricity amount of the cam ring 4 is maximum). FIG. 3 shows a case where the cam ring 4 is positioned at an end in the positive direction of y-axis (the eccentricity amount of the cam ring 4 is minimum).

Here, in the drawings, an axial direction of a driving shaft 2 is defined as x-axis, and a direction in which the driving shaft 2 is inserted into first and second housings 11, 12 is positive direction of x-axis. Further, an axial direction of a spring 201 that restrains or limits a movement (rock or tilt) of the cam ring 4 is defined as y-axis (see FIG. 2), and a direction in which the spring 201 (as a biasing means) forces or biases the cam ring 4 is the negative direction of y-axis. An axis orthogonal to x-axis and y-axis is z-axis, and a direction where an inlet vent “IN” is located is positive direction of z-axis.

The vane pump 1 has the driving shaft 2, a rotor 3, the cam ring 4, an adapter ring 5, and a pump body 10. The driving shaft 2 is connected with an engine and a pulley etc., and rotates integrally with the rotor 3 while being supported by the pump body 10.

As can be seen in FIGS. 2 and 3, a plurality of slots 31 are radially formed at the rotor 3 and arranged around a periphery of the rotor 3. This slot 31 is a groove formed in axial direction, and a vane 32 is provided in each slot 31. The vane 32 is inserted into the slot 31 so that the vane 32 can move or extend in radial direction. In an inner radial side end portion of each slot 31, a back-pressure chamber 33, in which a pressurized fluid is provided, is formed for forcing the vane 32 outward in the radial direction by the pressurized fluid.

The pump body 10 is formed of a first housing 11 and a second housing 12 (a second member). The first housing 11 is formed in a cup-shape having a bottom, which opens to the positive direction of x-axis. At a bottom portion 111 of the first housing 11, a disk shaped side plate or pressure plate 6 (a first member) is installed. The adapter ring 5, the cam ring 4 and the rotor 3 are installed or accommodated in a pump element accommodation portion 112 being an inner circumferential portion of the first housing 11, at the positive direction side of x-axis of the side plate 6.

The second housing 12 is in liquid-tight contact with the adapter ring 5, the cam ring 4 and the rotor 3 from positive direction side of x-axis. The adapter ring 5, the cam ring 4 and the rotor 3 are sandwiched between the side plate 6 and the second housing 12, and are held by these side plate 6 and second housing 12.

On an x-axis positive direction side surface 61 of the side plate 6 and/or on an x-axis negative direction side surface 120 of the second housing 12, inlet ports (or suction ports) 62 and 121 and also outlet ports (or discharge ports) 63 and 122 are respectively provided. The inlet ports 62, 121 open to an area inside a pump chamber “B (By−, By+)”, where a volume of the pump chamber increases by way of rotary motion of the rotor 3. The outlet ports 63, 122 open to an area inside the pump chamber “B (By−, By+)”, where the volume of the pump chamber decreases by way of the rotary motion of the rotor 3. These inlet and outlet ports are respectively communicated with the inlet vent “IN” and an outlet vent “OUT”, then supply and exhaust of working fluid for the pump chamber “B (By−, By+)” formed between the rotor 3 and the cam ring 4 are done.

The adapter ring 5 is an oval-shaped ring member that is substantially formed in an oval whose y-axis is major (longer) axis and whose z-axis is minor axis. As seen in FIGS. 2 and 3, the adapter ring 5 is installed or located inside the first housing 11, and the cam ring 4 is installed or located inside the adapter ring 5. During the pumping action, in order for the adapter ring 5 not to rotate in the first housing 11, the rotation of the adapter ring 5 with respect to the first housing 11 is restrained by a second seal member 40.

The cam ring 4 is a ring shaped member that is substantially formed in a perfect circle, and its diameter is substantially equal to a diameter of an inner circumference of the minor axis of the adapter ring 5. Therefore, since the cam ring 4 is installed inside the oval-shaped adapter ring 5, a hydraulic pressure chamber “A (A1, A2)” is defined between the inner circumference of the adapter ring 5 and an outer circumference of the cam ring 4 in a space outside the outer circumference of the cam ring 4. Further, the cam ring 4 can therefore move or rock or tilt inside the adapter ring 5 in y-axis direction (in more detail about this, the second seal member 40 acts as a rock fulcrum, and the cam ring 4 rocks about the second seal member 40 in y-axis direction).

At a top end portion in the positive direction of z-axis on an adapter ring inner circumferential surface 53, a seal member (a first seal member) 50 is provided. On the other hand, at a bottom end portion in negative direction of z-axis on the inner circumferential surface 53, a supporting surface “N” is formed. The adapter ring 5 supports the cam ring 4 and stops a movement in the negative direction of z-axis of the cam ring 4 by the supporting surface “N”. On the supporting surface “N”, the above mentioned pin-shaped second seal member 40 is provided. Further, the above mentioned hydraulic pressure chambers “A (A1, A2)” between the cam ring 4 and the adapter ring 5 is divided into two hydraulic pressure chambers by this second seal member 40 and the seal member 50 at the negative and positive direction sides of y-axis respectively, and a first hydraulic pressure chamber A1 and a second hydraulic pressure chamber A2 are defined.

Here, since the cam ring 4 rocks or tilts while rotating on the supporting surface “N”, each capacity or volume of the first and second hydraulic pressure chambers A1, A2 is varied. However, as can be seen in FIGS. 2 and 3, the supporting surface “N” at the negative direction side of z-axis is formed to be parallel to ξ-axis that is defined by turning y-axis in a clockwise direction on y-z plane. That is, the supporting surface “N” slants or slopes in the negative direction of z-axis as the supporting surface “N” extends in the positive direction of y-axis. And then, this sloping supporting surface “N” allows the cam ring 4 easily to rock or tilt in the positive direction of y-axis.

Outside diameter of the rotor 3 is smaller than that of a cam ring inner circumferential surface 41 of the cam ring 4, and the rotor 3 is installed or located inside the cam ring 4. The rotor 3 is provided so that an outer circumference of the rotor 3 does not touch the inner circumferential surface 41 even when the cam ring 4 rocks and a relative position between the rotor 3 and the cam ring 4 changes.

As can seen in FIG. 2, in a case where the cam ring 4 rocks and is positioned at the end in the negative direction of y-axis inside the adapter ring 5, a distance “L” between the cam ring inner circumferential surface 41 and the outer circumference of the rotor 3 becomes maximum. On the other hand, in a case where the cam ring 4 is positioned at the end in the positive direction of y-axis inside the adapter ring 5 as seen in FIG. 3, the distance becomes minimum.

Here, a length in the radial direction of the vane 32 is set to be longer than the maximum distance “L”. Therefore, the vane 32 always touches the inner circumferential surface 41 while being inserted in the slot 31 irrespective of the relative position between the rotor 3 and the cam ring 4. By this setting, the vane 32 always receives a back pressure from the back-pressure chamber 33, and liquid-tightly touches the cam ring inner circumferential surface 41.

Accordingly, liquid-tight spaces between the cam ring 4 and the rotor 3 are always defined by the plurality of the adjacent vanes 32, and the pump chamber “B (By−, By+)” is formed. Under a state where a center of the cam ring 4 shifts from a center of the rotor 3 by the rock of the cam ring 4 (that is, the rotor 3 and the cam ring 4 are under an eccentric position), volume of each pump chamber “B” varies by the rotation of the rotor 3.

The inlet ports 62, 121 and the outlet ports 63, 122, respectively provided at the side plate 6 and the second housing 12, are formed along the outer circumference of the rotor 3, and the supply and exhaust of the working fluid is done by the volume change of the each pump chamber “B”.

At an end portion in the positive direction of y-axis of the adapter ring 5, a radial-direction penetration hole or through hole (or bore, simply radial-direction hole) 51 is formed. Further, a plug member insertion hole 114 is formed at an end portion in the positive direction of y-axis of the first housing 11. Then, a plug member 70 formed in a cup-shape having a bottom is inserted into the plug member insertion hole 114, and an inside of the pump is insulated from an outside of the first and second housings 11, 12 and the liquid-tight inside of the pump is maintained.

The previously mentioned spring 201 is inserted into the plug member 70, and is secured in an inner circumference of the plug member 70 so that the spring 201 is extendable and contractible in y-axis direction. In more detail, the spring 201 penetrates the radial-direction hole 51 of the adapter ring 5 and touches or contacts the cam ring 4, then forces the cam ring 4 in the negative direction of y-axis.

The spring 201 is a spring that forces the cam ring 4 in the negative direction of y-axis, in which an amount of the rock of the cam ring 4 becomes maximum. Further, the spring 201 is the one that stabilizes the discharge amount (a rocking position of the cam ring 4) during a pump startup in which the pressure is not steady.

In the embodiment, an opening of the radial-direction hole 51 of the adapter ring 5 acts as a stopper that limits or restrains the rock in the positive direction of y-axis of the cam ring 4. However, the plug member 70 itself could penetrate the radial-direction hole 51 and protrude from the inner circumference of the adapter ring 5, and then act as the stopper for restraining the rock in the positive direction of y-axis of the cam ring 4 (see an embodiment 2).

As previously explained, the supporting surface “N”, which supports the cam ring 4 of the pump body 10, is formed so that the supporting surface “N” gradually separates from the first hydraulic pressure chamber A1 toward the second hydraulic pressure chamber A2 with respect to a virtual line “K-K” that is a straight line connecting a first median point “M1” and a second median point “M2”; the median point “M1” is positioned at a midpoint between an endpoint portion of the inlet ports 62, 121 and a starting-point portion of the outlet ports 63, 122, and the second median point “M2” is positioned at a midpoint between an endpoint portion of the outlet ports 63, 122 and a starting-point portion of the inlet ports 62, 121. That is to say, the supporting surface “N” is formed so that the supporting surface “N” slopes in the negative direction of z-axis and the positive direction of y-axis.

In a case where the vane pump 1 of the present invention is installed on a vehicle so that the virtual line “K-K” is horizontal, the cam ring 4 is apt to sink in the negative direction of z-axis due to an influence of discharge pressure “Pout” of the pump chamber “B”. However, in the present invention, the supporting surface “N” is formed so that the supporting surface “N” slopes in the negative direction of z-axis as the supporting surface “N” extends in the positive direction of y-axis on y-z plane. Thus, under a condition of low rotation and the maximum eccentricity of the cam ring 4, a portion or area on the supporting surface “N” where the cam ring 4 is supported is positioned at high position in z-axis direction against high pressure, while under a condition of high rotation and small eccentricity of the cam ring 4 and low pressure, the portion or area on the supporting surface “N” where the cam ring 4 is supported is positioned at low position in z-axis direction, and thereby cancel the sinking in the negative direction of z-axis of the cam ring 4. As a result, pulsation and noises under a range of the high rotation and low pressure and also under a range of the low rotation and high pressure can be suppressed.

[Supply of the Pressurized Fluid to First and Second Hydraulic Pressure Chambers]

As seen in FIGS. 2 and 3, a through hole 52 is provided at upper portion in positive direction of z-axis of the adapter ring 5, at a side of the seal member 50 in the positive direction of y-axis. This through hole 52 is communicated to a control valve 7 via an oil passage 113 provided inside the first housing 11. In addition, the through hole 52 is communicated with the second hydraulic pressure chamber A2 formed at the positive direction side of y-axis, then connects the second hydraulic pressure chamber A2 and the control valve 7. The oil passage 113 opens to a valve installation hole 115 that installs the control valve 7 therein, and a control or regulation pressure “Pv” is introduced into the second hydraulic pressure chamber A2 with the pumping action or drive. The control pressure “Pv” is introduced throughout a pressure-receiving-surface inside the second hydraulic pressure chamber A2.

The through hole 52 provided at the adapter ring 5 is formed at a middle portion of adapter ring's width in the axis direction, so that an outer circumferential surface of the adapter ring 5 acts as a seal surface and leakage can be reduced.

The control valve 7 connects or communicates with the outlet ports 63, 122 through oil passages 21 and 22. On the oil passage 22, an orifice 8 is provided, and a discharge pressure “Pout” of an upstream pressure of the orifice 8 and a downstream pressure “Pfb” of the orifice 8 are introduced into the control valve 7. Then, the control valve 7 is driven by a differential pressure (pressure difference) between these “Pout” and “Pfb” and a valve spring 7 a, and the control pressure “Pv” is produced or generated.

Thus, since the control pressure “Pv” is introduced into the second hydraulic pressure chamber A2 and this control pressure “Pv” is generated on the basis of an inlet pressure “Pin” and the discharge pressure “Pout”, a relationship between the control pressure “Pv” and the inlet pressure “Pin” is; control pressure “Pv”≧inlet pressure “Pin”.

On the other hand, the inlet pressure “Pin” is introduced into the first hydraulic pressure chamber A1 through a communication groove 64. This communication groove 64 is a radial-direction groove that is formed on the x-axis positive direction side surface 61 of the side plate (pressure plate) 6, and communicates or connects the inlet ports 62, 121 and the outer circumference of the cam ring 4. Accordingly, by this communication groove 64, the first hydraulic pressure chamber A1 is communicated with the inlet ports 62, 121, and the inlet pressure “Pin” is always introduced into the first hydraulic pressure chamber A1.

Hence, in the vane pump 1 of the present invention, only a hydraulic pressure “P2” of the second hydraulic pressure chamber A2 is controlled or regulated, while a hydraulic pressure “P1” of the first hydraulic pressure chamber A1 is not controlled, and the hydraulic pressure “P1” is always equal to the inlet pressure “Pin” (“P1”=“Pin”). Therefore, a pressure control and a flow amount control can be easy as compared with a case where both of the hydraulic pressures “P1” and “P2” of the first and second hydraulic pressure chambers A1, A2 are controlled.

Here, instead of the communication groove 64 provided at the side plate 6, a radial-direction groove could be provided at the second housing 12, and the inlet ports 62, 121 are communicated with the first hydraulic pressure chamber A1. Position of this radial-direction groove is not particularly limited to this. By this communication groove 64, since the working fluid that is discharged or flows out from the first hydraulic pressure chamber A1 is returned to a side of the inlet ports 62, 121, suction or inlet efficiency can be improved. Furthermore, the communication groove 64 can be easily provided by only forming the groove on the surface of the side plate 6.

[Rocking of Cam Ring]

When a pump inside pressure is exerted to a lower side in the negative direction of z-axis of the cam ring 4 (i.e. lower half of the cam ring 4), by an offset or a shift between a resultant force “Fp” and a cam ring rock or tilt supporting point “Na” on the supporting surface “N” of the adapter ring 5, a moment “Mp” is produced, which is exerted to the cam ring 4 and rotates the cam ring 4 in a direction of a small eccentricity (i.e. in the positive direction of y-axis). And this becomes an energizing or biasing force “F1” (simply, force “F1”). When the force “F1” is larger than a sum total force “F2” of the hydraulic pressure “P2” of the second hydraulic pressure chamber A2 and an energizing or biasing force in the negative direction of y-axis exerted to the cam ring 4 by the spring 201, the cam ring 4 tilts toward the second hydraulic pressure chamber A2. That is, the eccentricity amount of the cam ring 4, i.e. a difference or a shift between a center “O_(C)” of the cam ring 4 and a center “OR” of the rotor 3 becomes smaller, and the pump discharge amount is reduced (FIG. 3).

When the pump discharge amount is reduced, a flow amount of the fluid flowing through the orifice 8 via the oil passage 22 becomes low, and the pressure difference between the upstream pressure “Pout” and the downstream pressure “Pfb” becomes small. Then, a force of the valve spring 7 a overcomes the differential pressure (pressure difference), and the control valve 7 moves in the negative direction of y-axis (state of FIG. 2). And the “Pout” of high pressure is introduced to the control pressure “Pv”, the hydraulic pressure “P2” of the second hydraulic pressure chamber A2 therefore increases via the through hole 52. When the sum total force “F2” becomes larger than the force “F1” because of the increase of the hydraulic pressure “P2”, the cam ring 4 rocks or tilts toward the negative direction of y-axis (i.e. toward the first hydraulic pressure chamber A1). By this rocking movement or rocking motion of the cam ring 4, the eccentricity amount of the cam ring 4 increases and the discharge amount is increased. Further, when the discharge amount increases and the flow amount of the fluid flowing through the orifice 8 becomes high, the pressure difference between the upstream and downstream of the orifice 8 becomes large, and the control valve 7 moves in the positive direction of y-axis (FIG. 3), then the control pressure “Pv” and the hydraulic pressure “P2” of the second hydraulic pressure chamber A2 are lowered.

When the force “F1” in the positive direction of y-axis and the total force “F2” in the negative direction of y-axis substantially becomes equal to each other, a balance between the both forces in y-axis direction exerted to the cam ring 4 is struck, and the cam ring 4 stops or rests. Therefore, the pump can be controlled to keep a predetermined flow amount.

As explained above, the control pressure “Pv” is introduced into the second hydraulic pressure chamber A2. Meanwhile, as for the first hydraulic pressure chamber A1, the inlet pressure “Pin” is always introduced into the first hydraulic pressure chamber A1 and the hydraulic pressure “P1” of the first hydraulic pressure chamber A changes to the inlet pressure “Pin” instantly. Thus, this allows the rocking motion of the cam ring 4 toward the first hydraulic pressure chamber A1 with high response, and it is possible to improve the response of discharge amount control.

[Effect of the Embodiment 1]

(1) The variable displacement vane pump has the pump body 10, the driving shaft 2 rotatably supported by the pump body 10, the rotor 3 provided inside the pump body 10 and rotatably driven by the driving shaft 2, the plurality of vanes 32 radially extendably installed in respective slots 31 that are arranged in the circumferential direction in the rotor 3, the cam ring 4 rockably provided inside the pump body 10 and forming the plurality of pump chambers “B” at the inner circumference side of the cam ring 4 in cooperation with the rotor 3 and the vanes 32, the first and second members 6, 12 provided at both sides in the axial direction of the cam ring 4, the inlet ports 62, 121 provided at least one of the first and second members 6, 12 and opening to the area inside the pump chambers, where volumes of the plurality of pump chambers “B” increase by way of rotary motion of the rotor 3, the outlet ports 63, 122 provided at least one of the first and second members 6, 12 and opening to the area inside the pump chambers, where the volumes of the plurality of pump chambers “B” decrease by way of the rotary motion of the rotor 3, the seal member 50 provided at the outer circumference side of the cam ring 4 and defining the first hydraulic pressure chamber A1 located at the side where the pump discharge amount increases and the second hydraulic pressure chamber A2 located at the side where the pump discharge amount decreases in the space outside the outer circumference of the cam ring 4, and the control valve 7 controlling only the pressure of the second hydraulic pressure chamber A2.

Therefore, the inlet pressure “Pin” is introduced into the first hydraulic pressure chamber A1 and the first hydraulic pressure chamber A1 is kept to low pressure. Then, when increasing the discharge amount, by increasing the pressure of the second hydraulic pressure chamber A2, the cam ring 4 rocks toward the first hydraulic pressure chamber A1 instantly, and the response of the discharge amount control can be improved.

(2) The vane pump 1 further has the communication groove 64 communicating the first hydraulic pressure chamber A1 and the inlet ports 62, 121. Thus, the first hydraulic pressure chamber A1 and the inlet ports 62, 121, which are located at both sides of the cam ring 4, are connected to each other. Further, since the inlet pressure “Pin” is introduced into the first hydraulic pressure chamber A1 and the working fluid flowing out from the first hydraulic pressure chamber A1 is returned to the side of the inlet ports 62, 121, the suction efficiency can be improved.

(3) The communication groove 64 is provided on the surface of the side plate 6 or the second housing 12, which faces to the cam ring 4. Since the communication groove 64 is formed on the surface of the side plate 6 or the second housing 12, the communication groove 64 can be easily provided.

(4) (7) (11) The supporting surface “N” supporting the cam ring 4 has the slope that gradually separates from the second seal member 40 being the rock fulcrum of the cam ring 4 toward the second hydraulic pressure chamber A2 with respect to the reference line “K-K”connecting a rotation center point “O” of the driving shaft 2 and the median point “M” positioned at the midpoint between the endpoint portion of the inlet ports 62, 121 and the starting-point portion of the outlet ports 63, 122.

Thus, since the cam ring 4 is supported on the sloping supporting surface “N”, the noises can be suppressed under a low rotation and high discharge pressure condition and also a high rotation and low discharge pressure condition.

(5) The vane pump 1 further has the spring 201 that forces the cam ring 4 toward the first hydraulic pressure chamber A1. By this spring 201, it is possible to stabilize the discharge amount (the rocking position of the cam ring 4) during the pump startup in which the pressure is not steady.

(6) The rock of the cam ring 4 is controlled by controlling only one pressure of the second hydraulic pressure chamber A2 from the first and second hydraulic pressure chambers A1, A2. That is, the pressure of the second hydraulic pressure chamber A2 is controlled, while the pressure of the first hydraulic pressure chamber A1 is not controlled. Accordingly, the pressure control can be easy as compared with the case where both of the hydraulic pressures “P1” and “P2” of the first and second hydraulic pressure chambers A1, A2 are controlled.

(8) (12) The pump body 10 further has the ring-shaped or annular adapter ring 5 provided outside the outer circumference of the cam ring 4. Further, the control pressure “Pv” that controls or regulates the pressure of the second hydraulic pressure chamber A2 is introduced into the second hydraulic pressure chamber A2 via the through hole 52 formed at the adapter ring 5.

The through hole 52 is provided at the middle portion of adapter ring's width in the axis direction, so that the outer circumferential surface of the adapter ring 5 acts as the seal surface and leakage can be reduced.

(9) In the variable displacement vane pump having the orifice 8 provided on the oil passage communicating to the outlet ports 63, 122, and the control valve 7 into which the differential pressure between the upstream and downstream of the orifice 8 is introduced, the control valve 7 does not control the first hydraulic pressure chamber A1, but controls the second hydraulic pressure chamber A2. Since only the second hydraulic pressure chamber A2 is controlled, the flow amount control can be simplified.

(10) A pair of the first and second seal members 50, 40 are provided at the outer circumference of the cam ring 4, and define the first and second hydraulic pressure chambers A1, A2 around the outer circumference of the cam ring 4. Further, the control pressure “Pv” regulated by the control valve 7 is introduced throughout the pressure-receiving-surface inside the second hydraulic pressure chamber A2 defined by the first and second seal members 50, 40.

Since the control pressure “Pv” is introduced throughout the pressure-receiving-surface inside the second hydraulic pressure chamber A2, a pressure-receiving area becomes large. As a result, the control pressure “Pv” can be small. Hence, an amount of leakage from the second hydraulic pressure chamber A2 to low pressure side (the inlet ports 62, 121) can be suppressed.

Embodiment 2

[Control of Third Hydraulic Pressure Chamber]

An embodiment 2 will be explained with reference to FIG. 4. The structure of the embodiment 2 is basically same as the embodiment 1, so different structure or elements will be explained below.

In the embodiment 1, the hydraulic pressure “P2” of the second hydraulic pressure chamber A2 is controlled. Meanwhile, as for the embodiment 2, a piston 200 is provided as the plug member, instead of the plug member 70, and also a lid member 202 is provided. Then, a third hydraulic pressure chamber A3 is defined by an inner circumference of the piston 200 and the lid member 202. Further, the third hydraulic pressure chamber A3 is communicated with the control valve 7. With this, a hydraulic pressure “P3” of the third hydraulic pressure chamber A3 is controlled in the embodiment 2, while the hydraulic pressure “P2” of the second hydraulic pressure chamber A2 is controlled in the embodiment 1.

FIG. 4 is a sectional view in a radial direction of the vane pump 1 according to the embodiment 2. The piston 200 is formed in a cup-shape having a bottom, and is inserted into a piston insertion hole 114′ of the first housing 11 and the radial-direction hole 51 of the adapter ring 5 from a bottom portion 210 of the piston 200 in the negative direction of y-axis. In more detail, the piston 200 is slidably fitted into the piston insertion hole 114′ in the negative direction of y-axis with an outer circumference of the piston 200 and the piston insertion hole 114′ kept in liquid-tight contact.

The piston insertion hole 114′ is closed by the lid member 202 and liquid-tightly isolated or insulated from the outside of the pump. Then, as described above, the third hydraulic pressure chamber A3 is defined by the inner circumference of the piston 200 and the lid member 202. This third hydraulic pressure chamber A3 is located outside the outer circumference of the outlet ports 63, 122 in the space outside the outer circumference of the cam ring 4.

As can be seen in FIG. 4, the spring 201 is inserted into the piston 200, and is secured in an inner circumference of the piston 200 so that the spring 201 is extendable and contractible in y-axis direction. In more detail, one end of the spring 201 is secured to the lid member 202, and the spring 201 forces the piston 200 in the negative direction of y-axis.

The bottom portion 210 of the piston 200 penetrates the radial-direction hole 51 of the adapter ring 5 and touches or contacts the cam ring 4. The cam ring 4 is therefore forced in the negative direction of y-axis through the second hydraulic pressure chamber A2.

Further, in the embodiment 2, a communication passage 24 connecting the third hydraulic pressure chamber A3 and the control valve 7 is provided inside the first housing 11. The communication passage 24 opens to the valve installation hole 115 that installs the control valve 7 therein, and the control pressure “Pv” is introduced into the third hydraulic pressure chamber A3 with the pumping action.

In the same manner as the embodiment 1, the control valve 7 connects or communicates with the outlet ports 63, 122 through oil passages 21 and 22. On the oil passage 22, the orifice 8 is provided, and the discharge pressure “Pout” of the upstream pressure of the orifice 8 and the downstream pressure “Pfb” of the orifice 8 are introduced into the control valve 7. Then, the control valve 7 is driven by the differential pressure (pressure difference) between these “Pout” and “Pfb” and the valve spring 7 a, and the control pressure “Pv” is produced or generated.

Furthermore, in the same manner as the embodiment 1, the supporting surface “N” supporting the cam ring 4 slants in the negative direction of z-axis as the supporting surface “N” extends in the positive direction of y-axis, and the control pressure “Pv” is higher than the inlet pressure “Pin”. Therefore, by introducing the control pressure “Pv” into the third hydraulic pressure chamber A3, the cam ring 4 can be prevented from falling down toward the second hydraulic pressure chamber A2 (in the positive direction of y-axis).

[Effect of the Embodiment 2]

(13) In the variable displacement vane pump 1 having the orifice 8 formed on the oil passage 22 communicating to the outlet ports 63, 122, and the control valve 7 into which the differential pressure between the upstream and downstream of the orifice 8 is introduced, the control valve 7 controls only the pressure of the third hydraulic pressure chamber A3 that is located at the side where the discharge amount reduces by the rock of the cam ring 4 and into which the control pressure “Pv” is introduced, from the plurality of the hydraulic pressure chambers formed in the space outside the outer circumference of the cam ring 4.

Since the control valve 7 controls only the third hydraulic pressure chamber A3 into which the control pressure “Pv” being high pressure is introduced, the flow amount control can be simplified.

(14) The seal member 50 defines the first hydraulic pressure chamber A1 located at the side where the discharge amount increases by the rock of the cam ring 4 and the second and third hydraulic pressure chambers A2, A3 each located at the side where the discharge amount reduces by the rock of the cam ring 4 (namely in the positive direction of y-axis), each of which is formed in the space outside the outer circumference of the cam ring 4, and the control valve 7 controls the third hydraulic pressure chamber A3.

By this structure, the space located in the positive direction of y-axis outside the outer circumference of the cam ring 4 is separated into the second and third hydraulic pressure chambers A2 and A3, and the space of the third hydraulic pressure chamber A3 into which the control pressure “Pv” is introduced is defined. Thus, the flow of the working fluid becomes small, and a control controlling the small amount of the working fluid flow brings efficiency to the pump flow amount control.

(15) The control valve 7 introducing the control pressure “Pv” to the third hydraulic pressure chamber A3 is provided at the outer circumference side of the third hydraulic pressure chamber A3. Therefore, the communication passage 24 connecting the third hydraulic pressure chamber A3 and the control valve 7 can be simplified.

(17) The variable displacement vane pump further has the piston (the plug member) 200 liquid-tightly provided and movable in an axial direction thereof with respect to the cam ring 4, and the third hydraulic pressure chamber A3 is formed inside the piston 200. By this structure, leakage of the internal pressure of the third hydraulic pressure chamber A3 can be further suppressed.

Embodiment 3

An embodiment 3 will be explained with reference to FIG. 5. A basic configuration of the embodiment 3 is similar to the embodiments 1 and 2. In the embodiment 3, as can be seen in FIG. 5, the second hydraulic pressure chamber A2 of the embodiment 1 is separated into two hydraulic pressure chambers. One is a second hydraulic pressure chamber A2, and the other is a third hydraulic pressure chamber A3, and only hydraulic pressure “P3” of the third hydraulic pressure chamber A3 is controlled.

[Defining Third Hydraulic Pressure Chamber A3 by Seal Member]

FIG. 5 is a sectional view in a radial direction of the vane pump 1 according to the embodiment 3. Between the cam ring 4 and the adapter ring 5 at the positive direction side of y-axis of the second seal member 40, a third seal member 300 is provided for defining the second and third hydraulic pressure chambers A2 and A3. In the embodiment 3, the chamber located in the positive direction side of z-axis of the third seal member 300 is defined as the second hydraulic pressure chamber A2, and the chamber located in the negative direction side of z-axis of the third seal member 300 is defined as the third hydraulic pressure chamber A3. Here, in the embodiment 3, the seal member 300 is provided in the negative direction side of z-axis of the plug member 70. However, it could be provided in the positive direction side of z-axis of the plug member 70 (see an embodiment 3-1).

The third hydraulic pressure chamber A3 is connected to the control valve 7 through an oil passage 25, and the control pressure “Pv” is introduced into the third hydraulic pressure chamber A3. On the other hand, the second hydraulic pressure chamber A2 does not communicate with the inlet and outlet sides and the control valve 7, and a leakage pressure flows into the second hydraulic pressure chamber A2. Meanwhile, as for the first hydraulic pressure chamber A1, in the same manner as the embodiment 1, the inlet pressure “Pin” is introduced into the first hydraulic pressure chamber A1 through the communication groove 64.

Accordingly, the cam ring 4 is forced in the positive direction of y-axis by the pump inside pressure. On the other hand, the cam ring 4 is forced in the negative direction of y-axis by the control pressure “Pv” introduced into the third hydraulic pressure chamber A3 provided at the positive direction side of y-axis.

[Detail of the Seal Member]

The seal member 300 has a rock fulcrum 310 and a projecting portion 320 that projects from the rock fulcrum 310. The rock fulcrum 310 is circular in cross section, and is buried in a recessed or depressed portion 54 that is formed on the adapter ring inner circumferential surface 53 so that the rock fulcrum 310 is rotatable in the y-z plane.

The projecting portion 320 protrudes from the adapter ring 5, and rotates inside the third hydraulic pressure chamber A3 about the rock fulcrum 310 as a rotation center. However, the rotation in the clockwise direction of the projecting portion 320 is stopped by a rotation-limiting portion 55, while the rotation in the counterclockwise direction is stopped by a holding or retaining portion 56.

Here, under a condition in which the control pressure “Pv” is not introduced into the third hydraulic pressure chamber A3, a top end portion 321 of the projecting portion 320 is set to protrude on an inner radial side of the adapter ring inner circumferential surface 53, and the seal member 300 is set to fall down to the negative direction side of y-axis. When the discharge pressure starts to be introduced into the third hydraulic pressure chamber A3 at the pump start, the working fluid flows from the third hydraulic pressure chamber A3 into the side of the second hydraulic pressure chamber A2.

And when this flow of the working fluid strikes against the projecting portion 320, the seal member 300 rises in the positive direction of y-axis and in the positive direction of z-axis from the state where the seal member 300 falls down. By this, the seal member 300 stopping the cam ring 4 maintains the control pressure “Pv” inside the third hydraulic pressure chamber A3, and a sealing performance is secured.

The seal member 300 is formed so that the sealing performance of the seal member 300 is secured by the pressure. Because of this, a sealing force varies depending on the pressure. Hence, this prevents the sealing force from being too strong under the low pressure condition in which the leakage is small and also prevents the lack of the sealing force (biasing force) under the high pressure condition in which the leakage is large, in contrast to the spring whose biasing force is constant.

The projecting portion 320 always touches the outer circumference of the cam ring 4 irrespective of the rocking position of the cam ring 4. The seal member 300 receives the control pressure “Pv” through the oil passage 25, and rotates in the clockwise direction. Then, since the projecting portion 320 touches the outer circumference of the cam ring 4, the third hydraulic pressure chamber A3 is defined.

As can be seen in FIG. 5, a stopper portion 57, which protrudes toward the inside of the pump, is provided in the positive direction side of z-axis of the recessed portion 54 of the adapter ring 5. This stopper portion 57 is formed to be thicker than other portions in the adapter ring 5, so that a strength around the recessed portion 54 can be improved.

[Eccentricity Amount of Cam Ring and Working of Hydraulic Pressure Chamber]

The variable displacement vane pump, in which the inlet pressure is always introduced into the second hydraulic pressure chamber A2 provided at the side where the pump volume reduces, tends to lack the force biasing the cam ring 4 in the negative direction of y-axis, because the inlet pressure is always introduced into the second hydraulic pressure chamber A2. In particular, in the case where the supporting surface “N” of the adapter ring 5 slopes toward the negative direction of z-axis and the positive direction of y-axis, like the vane pump of the present invention, there is a possibility that the cam ring 4 will fall down or tilt to the side of the second hydraulic pressure chamber A2 and the pump discharge amount will reduce unintentionally or unexpectedly.

Therefore, in the embodiment 3, the third seal member 300 is provided at the positive direction side of y-axis of the second seal member 40 for defining the third hydraulic pressure chamber A3, then the control pressure “Pv” is introduced into the third hydraulic pressure chamber A3, and the cam ring 4 is forced in the negative direction of y-axis. With this, the force biasing the cam ring 4 in the negative direction of y-axis can be secured, and the unexpected reduction of the pump discharge amount, due to the falling down to the positive direction side of y-axis of the cam ring 4, can be prevented.

[Effect of the Embodiment 3]

(18) The third seal member 300 defining the second and third hydraulic pressure chambers A2 and A3 is forced toward the cam ring 4 by the control pressure “Pv” introduced into the third hydraulic pressure chamber A3, and the sealing performance is secured.

Since the third seal member 300 is formed so that the sealing performance can be secured, the suitable sealing force according to the pressure is obtained. Therefore, this can prevent the sealing force from being too strong under the low pressure condition in which the leakage is small and also prevent the lack of the sealing force (biasing force) under the high pressure condition in which the leakage is large, as compared with the spring whose biasing force is constant.

(19) In the embodiment 3 as well, the supporting surface “N” supporting the cam ring 4 has the slope that gradually separates from the second seal member 40 being the rock fulcrum of the cam ring 4 toward the second hydraulic pressure chamber A2 with respect to the reference line “K-K” connecting a rotation center point “O” of the driving shaft 2 and the median point “M” positioned at the midpoint between the endpoint portion of the inlet ports 62, 121 and the starting-point portion of the outlet ports 63, 122. Thus, since the cam ring 4 is supported on the sloping supporting surface “N”, the noises can be suppressed under a low rotation and high discharge pressure condition and a high rotation and low discharge pressure condition.

(20) The vane pump further has the communication groove 64 communicating the inlet ports 62, 121 and the first hydraulic pressure chamber A1 that is located at the side where the discharge amount increases, from the plurality of the hydraulic pressure chambers A1 A3 formed in the space outside the outer circumference of the cam ring 4.

Thus, the first hydraulic pressure chamber A1 and the inlet ports 62, 121, which are located at both sides of the cam ring 4, are connected to each other. Further, since the inlet pressure “Pin” is introduced into the first hydraulic pressure chamber A1 and the working fluid that flows out from the first hydraulic pressure chamber A1 is returned to the side of the inlet ports 62, 121, the suction efficiency can be improved.

The third hydraulic pressure chamber A3 is formed outside the outer circumference of the outlet ports 63, 122. Since the third hydraulic pressure chamber A3 into which the control pressure “Pv” of high pressure is introduced is provided outside the outer circumference of the outlet ports 63, 122, pressure leakage from the third hydraulic pressure chamber A3 can be suppressed, and there is no pressure leakage to the side of the inlet ports 62, 121 (the low pressure side). In addition, since the third hydraulic pressure chamber A3 is formed inside the piston 200, the leakage is further reduced.

(16) The third hydraulic pressure chamber A3 is formed at the outer circumference side of the outer circumference of the outlet ports 63, 122. Since the third hydraulic pressure chamber A3 into which the control pressure “Pv” of high pressure is introduced is provided outside the outer circumference of the outlet ports 63, 122, pressure leakage from the third hydraulic pressure chamber A3 can be suppressed (the pressure does not leak to the side of the inlet ports 62, 121 (the low pressure side)).

The following is a modification of the embodiment 3.

Embodiment 3-1

FIG. 6 is the modification in which the seal member 300 is provided in the positive direction side of z-axis of the plug member 70. Since the seal member 300 is positioned apart from the supporting surface “N”, the pressure-receiving area of the third hydraulic pressure chamber A3 becomes small, then the leakage can be reduced. Furthermore, since the seal member 300 is provided at close to the valve, the oil passage for communicating or connecting these seal member 300 and the valve can be easily formed.

This application is based on a prior Japanese Patent Application No. 2006-079912 filed on Mar. 23, 2006. The entire contents of this Japanese Patent Application No. 2006-079912 are hereby incorporated by reference.

Although the invention has been described above by reference to certain embodiment of the invention, the invention is not limited to the embodiment described above. Further, design changes or engineering-change based on the embodiment are also included in the invention. Modifications and variations of the embodiment will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

1. A variable displacement vane pump comprising: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring; and a control valve controlling only a pressure of the second hydraulic pressure chamber.
 2. The variable displacement vane pump as claimed in claim 1, further comprising: a communication groove communicating the first hydraulic pressure chamber and the inlet port.
 3. The variable displacement vane pump as claimed in claim 2, wherein: the communication groove is formed on a surface of one of the first and second members, which faces to the cam ring.
 4. The variable displacement vane pump as claimed in claim 2, wherein: the cam ring is supported on a supporting surface inside the pump body, and wherein the supporting surface has a slope that gradually separates from a rock fulcrum of the cam ring toward the second hydraulic pressure chamber with respect to a reference line connecting a rotation center of the driving shaft and a median point positioned at a midpoint between an endpoint portion of the inlet port and a starting-point portion of the outlet port.
 5. The variable displacement vane pump as claimed in claim 2, further comprising: biasing means for biasing the cam ring toward the first hydraulic pressure chamber.
 6. A variable displacement vane pump comprising: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; and a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring, and the rocking motion of the cam ring being controlled by controlling only one pressure of the second hydraulic pressure chamber from the first and second hydraulic pressure chambers.
 7. The variable displacement vane pump as claimed in claim 6, wherein: the cam ring is supported on a supporting surface inside the pump body, and wherein the supporting surface has a slope that gradually separates from a rock fulcrum of the cam ring toward the second hydraulic pressure chamber with respect to a reference line connecting a rotation center of the driving shaft and a median point positioned at a midpoint between an endpoint portion of the inlet port and a starting-point portion of the outlet port.
 8. The variable displacement vane pump as claimed in claim 6, wherein: the pump body has an annular adapter ring provided outside the outer circumference of the cam ring, and a control pressure that regulates the pressure of the second hydraulic pressure chamber is introduced into the second hydraulic pressure chamber via a through hole formed at the adapter ring.
 9. A variable displacement vane pump comprising: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring; an orifice provided on an oil passage that communicates to the outlet port; and a control valve into which a differential pressure between upstream and downstream of the orifice is introduced, and the control valve not controlling the first hydraulic pressure chamber but controlling the second hydraulic pressure chamber.
 10. The variable displacement vane pump as claimed in claim 9, wherein: the seal member is formed of a pair of seal members provided at the outer circumference of the cam ring and define the first and second hydraulic pressure chambers around the outer circumference of the cam ring, and a control pressure regulated by the control valve is introduced throughout a pressure-receiving-surface inside the second hydraulic pressure chamber defined by the pair of the seal members.
 11. The variable displacement vane pump as claimed in claim 9, wherein: the cam ring is supported on a supporting surface inside the pump body, and wherein the supporting surface has a slope that gradually separates from a rock fulcrum of the cam ring toward the second hydraulic pressure chamber with respect to a reference line connecting a rotation center of the driving shaft and a median point positioned at a midpoint between an endpoint portion of the inlet port and a starting-point portion of the outlet port.
 12. The variable displacement vane pump as claimed in claim 9, wherein: the pump body has an annular adapter ring provided outside the outer circumference of the cam ring, and the control pressure that regulates the pressure of the second hydraulic pressure chamber is introduced into the second hydraulic pressure chamber via a through hole formed at the adapter ring.
 13. A variable displacement vane pump comprising: a pump body; a driving shaft rotatably supported by the pump body; a rotor provided inside the pump body and rotatably driven by the driving shaft; a plurality of vanes radially extendably installed in respective slots that are arranged in a circumferential direction in the rotor; a cam ring rockably provided inside the pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes; a first and a second members provided at both sides in an axial direction of the cam ring; an inlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where volumes of the plurality of pump chambers increase by way of rotary motion of the rotor; an outlet port provided at least one of the first and second members and opening to an area inside the pump chambers, where the volumes of the plurality of pump chambers decrease by way of the rotary motion of the rotor; a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring; an orifice provided on an oil passage that communicates to the outlet port; and a control valve into which a differential pressure between upstream and downstream of the orifice is introduced, and the control valve controlling only a pressure of hydraulic pressure chamber that is located at the side where the discharge amount decreases by the rock of the cam ring and into which a control pressure is introduced, from the plurality of the hydraulic pressure chambers formed in the space outside the outer circumference of the cam ring.
 14. The variable displacement vane pump as claimed in claim 13, wherein: the seal member defines the first hydraulic pressure chamber formed at the side where the discharge amount increases by the rock of the cam ring and the second and also a third hydraulic pressure chambers formed at the side where the discharge amount decreases by the rock of the cam ring around the outer circumference of the cam ring, and the control valve controls the third hydraulic pressure chamber.
 15. The variable displacement vane pump as claimed in claim 14, wherein: the control valve is provided at an outer circumference side of the third hydraulic pressure chamber.
 16. The variable displacement vane pump as claimed in claim 14, wherein: the third hydraulic pressure chamber is formed at an outer circumference side of the outlet port.
 17. The variable displacement vane pump as claimed in claim 14, further comprising: a plug member liquid-tightly provided and movable in an axial direction thereof with respect to the cam ring, and wherein the third hydraulic pressure chamber is formed inside the plug member.
 18. The variable displacement vane pump as claimed in claim 14, wherein: the seal member is formed of a first, a second and a third seal members provided outside the outer circumference of the cam ring, the first and second seal members define the first hydraulic pressure chamber and the second and the third hydraulic pressure chambers around the outer circumference of the cam ring, the third seal member defines the second hydraulic pressure chamber and the third hydraulic pressure chamber around the outer circumference of the cam ring, and the third seal member is forced toward the cam ring by a pressure introduced into the third hydraulic pressure chamber, and sealing performance is secured.
 19. The variable displacement vane pump as claimed in claim 13, wherein: the cam ring is supported on a supporting surface inside the pump body, and wherein the supporting surface has a slope that gradually separates, toward the side where the pump discharge amount decreases, with respect to a reference line connecting a rotation center of the driving shaft and a median point positioned at a midpoint between an endpoint portion of the inlet port and a starting-point portion of the outlet port.
 20. The variable displacement vane pump as claimed in claim 13, further comprising: a communication groove communicating the inlet port and the hydraulic pressure chamber that is located at the side where the discharge amount increases, from the plurality of the hydraulic pressure chambers formed in the space outside the outer circumference of the cam ring. 